Passing custom headers with the new API keys

It seems like custom headers are being stripped when passed with the new api keys, publishable or not. Ideas, suggestions?

   headers: {
      'apikey': <key>,
      'x-custom-header': <header>,
      'Content-Type': 'application/json',
    },

   headers: {
      'apikey': <key>,
      'x-custom-header': <header>,
      'Content-Type': 'application/json',
    },

TIA!